英国剑桥大学 (University of Cambridge)：液晶图片偶氮染料的新发展

27.1: Invited Paper: New Developments in Liquid Crystal Photo-Aligning by Azo-Dyes
特邀报告：液晶图片偶氮染料的新发展
V. G. Chigrinov, H.S. Kwok
Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong Hirokazu Takada, Haruyoshi Takatsu
Corporate R&D Division, Dainippon Ink and Chemicals Incorporated, Japan
Abstract
摘要
Liquid crystal photo-alignment using azo-dyes is reviewed. This alignment method is very different from previously reported ones, such as photo-crosslinking, photo degradation and photo-isomerization. It will be shown that this photo-aligning method can provide a controllable pretilt angle and strong anchoring energy of the liquid crystal cell, as well as high thermal and UV stability. The application of this method to the alignment and fabrication of various types of liquid crystal displays is also discussed.
液晶光配向使用偶氮染料已经复习过了。此对应方法与如先前的报道是非常不同的，例如光交联，光降解和光异构化。它将会这个照片调心的方法中显示，可以提供一个可控的预倾角和强锚定能的液晶单元，以及高热和UV稳定性。在此方法中，对不同类型的液晶显示器的取向和制造中的应用进行了讨论。
1. Introduction
介绍
The field of liquid crystal (LC) photo-alignment is very rapidly developing and a vast amount of the new materials, techniques and LCD prototypes based on photo-alignment (PA) technology have appeared recently. However, despite these potential advantages, the application of PA to LCD production is still limited to the laboratory. Large scale deployment of PA is hampered by the lack of a good material and by long term stability, not to mention the la ck of suitable mass production scale equipment. The effect of LC photoalignment is a direct consequence of the appearance of the photo-induced optical anisotropy and dichroic absorption in thin amorphous films, formed by molecular units with anisotropic absorption properties.
液晶（LC）领域光配向发展非常迅速，基于光配向 （PA）科技的大量新材料，科技和LCD原型最近也都相继出现。然而，尽管有这些潜在的优势，PA到LCD生产的应用仍然仅限于实验室。
The first publication on LC photo-alignment appeared in 1988, which discussed the application of a reversible cis-transisomerization of the azo-benzene molecular layers [2]. The optical control of LC alignment was made by changing the wavelength of the non-polarized light illumination [2].Later it was shown that the alignment of a liquid crystal medium could be made by illuminating a dye doped polymer alignment layer with polarized light [3]. LC molecules in contact with the illuminated area were homogeneously aligned perpendicular to the direction of the laser polarization and remained aligned in the absence of the laser light. Subsequently, LC photo-alignment was also achieved using cinnamoyl side-chain polymers [4,5] and polyimide aligning agents [6]. More recently, a new class of azo-dyes have also been studied with excellent results [10,11]. In this paper, we shall review the physical mechanism of this alignment process and report some new results related to the processing conditions using these azo-dyes. In particular, we discuss the conditions where the light dosage is greatly reduced, to less than 50mJ/cm2. Applications of this new PA material to various types of LCD will also be reviewed. #p#分页标题#e#
最近，一类新的偶氮染料也被研究出来了，而且具效果很好。在本文中，我们将回顾这个校准过程的物理机制和相关的加工条件下使用这些偶氮染料报告中的一些新的结果。特别是，光剂量大大降低，低于50mJ/cm2。这种新的PA材料应用于各种类型的LCD也将进行考察。
2. Results
结果
2.1  Azo-dye aligning layers
Photo-alignment can generally be classified into four categories according to their mechanism.
根据光取向的机制，光取向大致可以分为四类。
They are (i) photochemically reversible cis-trans isomeriz ation in azo-dye containing polymers, monolayers and pure dye films [12,13]; (ii) photochemical crosslinking in preferred directions of polymer precursors, such as cinnamoyl side-chain polymers [4,5]; (iii) photodegradation and orientational bond breaking in polyimide materials [14,15]; and (iv) pure reorientation of the azo-dye chromophore molecules or azo-dye  molecular solvates due to the diffusion under the action of polarized light [10,11]. Recently the method of repeated cis-trans photoisomerization reaction resulting in the reorientation of the backbone structure of polyamic acid contained azobenzene units was reported [16,17].
最近，据报道，顺反光致异构化反应的方法导致了包含偶氮单位的聚酰胺酸主体结构的再定位。
We believe that the method (iv) with pure diffusion reorientation of the azo-dye chromophore molecules or azo-dye molecular solvates is the most promising one for large scale applications. In this case the azo- dye molecules, are tending to align their long axes perpendicular to the UV-light polarization resulting in anisotropic dichroism or birefringence of the PA film [18]. Actually the photo-aligned azo-dye molecules produce a very smooth and uniform structure with the thickness of several nanometers controlled by the concentration of the azo-dye in an organic solvent e.g. N,N-dimethylformamide (DMF) [11].
实际上，照片对齐偶氮染料分子产生一个非常光滑，均匀的结构，由偶氮染料的浓度控制在有机溶剂中，例如几纳米的厚度N，N-二甲基甲酰胺（DMF）[11]。
The change of the azo-dye concentration between 0.4 and 1.3  http://ukthesis.org/ygsslwdx/  wt/wt % concentration results in the thickness variation of the photo-alignment layer between 3 and 12 nm [19].
偶氮染料的浓度在0.4和1.3％浓度的变化导致了3至12纳米的光取向层的厚度变化。